1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to a flat panel display with a larger display region and a reduced line resistance.
2. Description of the Related Art
Flat panel displays such as liquid crystal displays, organic electroluminescent displays, and inorganic electroluminescent displays are divided into a passive matrix (PM)-type and an active matrix (AM)-type according to their driving methods. PM flat panel displays have a simple intersection structure of column electrodes (anodes) and row electrodes (cathodes). Scanning signals output from a row driving circuit are supplied to cathodes. At this time, only one row is selected from multiple rows. Then, a column driving circuit outputs data signals, which are then inputted into each pixel. On the other hand, AM flat panel displays control a signal to be sent to each pixel using a thin film transistor (TFT). Due to high signal processing performance, the AM flat panel displays have been widely used as displays for moving images.
Among flat panel displays, organic electroluminescent displays comprise a light emission layer comprising an organic material, which is interposed between an anode and a cathode. When positive and negative voltages are respectively applied to these electrodes, holes from the anode migrate toward the light emission layer via a hole transport layer and electrons from the cathode are injected into the light emission layer via an electron transport layer. At this time, the electrons and the holes recombine with each other at the light emission layer to generate an exciton. When the exciton is changed from an excited state to a ground state, a fluorescent molecule of the light emission layer emits light, which displays an image. When the organic electroluminescent displays are provided with pixels emitting red (R), green (R), and blue (B) light, full color organic electroluminescent displays that display full color may be realized.
However, such organic electroluminescent displays have a limitation in that organic films such as a light emission layer are very susceptible to moisture. In this regard, attempts have been made to prevent the entry of external moisture into a light emission layer and protect the display regions of the organic electroluminescent displays from external physical impacts. As an example thereof, a sealing process is known for a display region, wherein the process uses a substrate or a metal cap.
FIGS. 1 and 2 show a conventional active matrix organic electroluminescent display.
Referring to FIGS. 1 and 2, an active matrix organic electroluminescent display has a predetermined display region 2 comprising organic electroluminescent devices. The display region 2 is formed on a transparent insulating substrate 11 and is sealed by bonding a covering member 12, such as a metal cap, to the substrate 11 by utilizing a sealing member 13 made of a sealing material. In the display region 2, organic electroluminescent devices, together with thin film transistors, are arranged to form multiple pixels. The top portion of the display region 2 is formed with a cathode 243, one electrode of the organic electroluminescent devices. The cathode 243 is connected to an external terminal region 3 through an electrode power line 42 installed at one side of the display region 2. Multiple VDD lines 25 are also arranged in the display region 2. The VDD lines 25 are connected to the terminal region 3 through a driving power line 41 installed outside the display region 2 to supply a driving potential power and/or a source current to the display region 2. In addition, a vertical circuit 51 and a horizontal circuit 52 are installed outside the display region 2 to send a signal to thin film transistors of the display region 2. The vertical and horizontal circuits 51 and 52 are connected to the terminal region 3 through circuit lines 43 and 44, respectively.
All regions of the above-described active matrix organic electroluminescent display, including the display region 2, the power lines 41 and 42, and vertical and horizontal circuits 51 and 52, except for the terminal region 3, are covered with the covering member 12 such as a metal cap and then sealed. Therefore, together with the display region 2 displaying an image, regions that take no part in an image display, i.e., the power lines 41 and 42 and vertical and horizontal circuits 51 and 52 are also present inside the covering member 12. This leads to a decrease in the ratio of the display region 2 intended for light emission to the total size of an organic electroluminescent display. Therefore, a dead space, which is a non-emission region, increases, thus lowering a light emission efficiency.
In addition, for the foregoing reason, in the organic electroluminescent display shown in FIGS. 1 and 2, the power lines 41 and 42, which connect the display region 2 to the terminal region 3, must have a very small width. Due to such a very small width, the organic electroluminescent display undergoes an increase of resistance in the power lines.
These are common limitations for active matrix organic electroluminescent displays. The organic electroluminescent displays disclosed in Japanese Patent Laid-Open Publication Nos. 2000-173779 and 2000-173766 also have the above-described limitations.
Meanwhile, U.S. Pat. No. 6,359,606 discloses an active matrix organic electroluminescent display, the entire surface of which is covered with a protective film, instead of using a covering member, such as a metal cap and a glass substrate. The protective film prevents the entry of moisture or oxygen, and thus inhibits deterioration of organic electroluminescent devices.
However, since the above active matrix type display protects inner devices thereof using a thin protective film, the inner devices of the display cannot be protected sufficiently from external impact. Also, since organic electroluminescent displays require complete prevention against exposure to moisture, such an aspect cannot be accomplished only using the protective film. This fact is supported by U.S. Pat. No. 5,882,761, in which an organic electroluminescent display further comprises a moisture absorbent inside a metal cap or a glass substrate. In addition, displays only using such a thin protective film cannot be used as front-surface emission types and both-surface emission types that project an image toward a sealing member.
Korean Patent Laid-Open Publication No. 2002-9498 discloses an electroluminescent display sealed with a covering member and a sealing member. The display comprises multiple lines interconnected in parallel, which are arranged between the sealing member and a substrate. However, since the multiple lines have a small width and are interconnected in parallel, there are problems in that a line structure is complicated, and a line resistance increases.